* {
    margin: 0;
    padding: 0;
}

.head-top {
    background-color: red;
    height: 40px;
}

li {
    list-style-type: none;
}

.head-top>div>ul {
    float: right;
    height: 40px;
    display: flex;
    align-items: center;
}

.head-top>div>ul>li {
    display: inline-block;
    width: 100px;
    margin-right: 20px;
}

.head-top>div>ul>li:nth-child(4) {
    position: relative;
}

.head-top>div>ul>li>ul {
    position: absolute;
    top: 30px;
    right: 0px;
}

.sub-nav {
    width: 120px;
    height: 200px;
    background-color: green;
    text-align: center;
    display: none;
}

.head-top>div>ul>li:nth-child(4):hover>.sub-nav {
    display: block;
}